Apparatus for evaporating liquid oxygen



June 4, 1946@l J. A. MATHIS ET AL,

APPARATUS FOR EVAPORATING LIQUID OXYGEN vFiled. Dec. 28, 1942 LE-llill .lill l l Il Il Il INVENTORS. .Jahn A- MaH-i. 5 HD1 ELT-L Mil an B Y Y ZWTORIEQA Patented June 4, 1946 22401551 APPRATUS FOR EVAPQRAIING LIQUID XYGEN John ill. Mathis and Boland Wn Milan, Pinchneyville, 111

limpplioation December 23, 1942, Serial No. 470,384; n

itil. Zit-439) e come. i

This invention relates to an improved appa=- ratos for supplying a controlled dow oi gaseous oxygen under pressure by the controlled 'evaporation of liquid oxygen. More speciilcally, this invention is an improvement oi our prior inven tion relating to a method and apparatus for evaporating liquid oxygen described and claimed in the United States Patent No. Ziodfiii, oi May i6, 1939.

Since our prior invention, alcove identified, has fairly established the'ieasibility oi andthe aok vantages in the method oi dispensing gaseous oxygen from liquid oxygen by manually controlling its rate ci evaporation, new becomes desirahle to utilize this method for supplying oxygen to the crew' ci ciali altitude aircraft.. in adapting this prior method for use in this particu ular field, several important and novel features had to he incorporated in the apparatus prem viously employed to rca-re its operation sufficiently satisfactory use in its new environment. For example, it was found necessary to enclose the liquid oxygen in a container sealed. ogainst the pressure present therein and to supply the gaseous oxygen under pressure. Furthermore, it was iound that the pressure could he maintained substantially constant oy utilising; a heating'ele=l ment to raise the temperature oi the liquid oxygen thereby increasing its rate oi? evaporation. and iurtlier to control the energization oi the said heating element in response to variations in the vapor pressure acting on, the surface oi. said liquid oxygen.

It is, therefore, a primary objective of this in vention to provide means for dispensing gaseous oxygen by controlling the temperature and rate of evaporation of said liquid owgen in accordance with the pressure ci the vapor acting upon its surface., 1

.As is well ltnown, the vapor pressure acting upon a body of liquid is a function of its temperature and will increase as the temperature iri-= creases; consequently, the vapor may be caused to return to liquid by increasing the pressure ci the vapor acting upon the liquid to a value in excess of that normally existing at a particular temperature when the vapor and the liquid are in equilibrium. Thus, by utillalru,F a heat exchange device in a dispensing conduit leading; from the sealed container for said liquid oxygen to subject liquid oxygen escaping;r through the conduit to a. temperature considerably in excess of the temperature oi the liquid within the container it is possible to permit the apparatus to operate in an inverted position which is very 2 desirable when the apparatus is installed inL aircraft. That is, by utiiizine such a heat exchange device in the said dispensing conduit, e. small quantity of liquid may initially escape into the conduit when the container becomes inverted, lout this liquid will be immediately evaporated. by the heat supplied thereto through the heating exchange device'and since the temperature of the heat exchange device exceeds the temperature oi the body of liquid oxygen, the vapor pressure Within the conduit produced by the evaporation of this small but sufdcient amount oi liquid will exceed the vapor pressure within the Dewar iiaslr. The evaporated liquid thus raises the pressure within the dosi; and since the temperature oi the liquid within the iiaslr is not high enough to GEB vto

maintain such a vvapor pressure, the vapor will return to liquid. Thus, no liquid can he dispensed through the conduit when the :dass inverted because in escondidof into the conduit, he liquid evaporates building up a pressure in the conduit and nasi: higher than that which can be maintained by vapor in the flask at tice te'im perature oi the liquid mass therein, thereby de1A stroying the conditions ci equilibrium causingr the vapor to return to liquid.

Consequently, we propose as an object of this invention to provide a heat exchange device :lu the dispensing conduit of si container for evap-J orating liquid'oxygen to permit inverted opere-s tion oi the said container.

It is a further object of this invention to dise pense gaseous oxygen at substantially constant pressure irrespective of whether or not the liquid oxygen container is maintained in an inverted f periods of time without an appreciable diderence in pressure.

Other objectives and advantages of the invention will become apparent from the specication as the specific features o f this invention are hereinafter described in detail in connection with the accompanying drawing in which:

Fig. 1 is an elevational view oi a vertical secu tion showing the apparatus of the present invenu tion installed upon a flask containing liquid oxy- Een;

Fig. 2 is a wiring diagram of the circuit connections for the electrical heating element; and

Fig. 3 is a side view in elevation of the capacity securing means for the flask.

Referring particularly to the drawing, the reference character I indicates the usual Dewar flask provided with the usual outlet neck 2. The flask is resiliently and insulatedly supported in a metallic housing 3 to preventl breakage resulting from sudden shock and to inhibit direct transmission of heat, by means of the spring 4 which as shown is resiliently compressed against the inside housing 3 and the outer surface of the ask I and by means of the compression spring 5 retained in position between the collar 8 secured to the neck portion 2 of the Dewar flask and the flange 1 supported within the neck portion 8 of the housing 3. The cap I0 has an inner frusto-conical surface II of ground brass which provides a gas-tight connection with the ferruled rim I2 of the flask I. Secured to the cap I0 is a. cabinet l5 which has an open end to permit the free circulation or'convection of air therethrough and an elongated brass tube I4. The brass tube I4 is preferably inserted into the cap I so that its flanged surface will securely hold the cabinet l in assembled position between the top lateral surface of the cap and the lateral surface of the flange.

Figs. 1 and 3 show in detail the construction means by which the ground surface II of the cap I0 is held in gas-tight contact with the ierruled rim of the flask to seal the cap and flask against the vapor pressure maintained therein. As illustrated, the cap I0 is provided with a cylindrically and radially extending flange I6 formed at its lower end against which is pressed the split collar I1 having a pair of projecting ears I8 and I3. To the ears I8 and I9 of the collar are attached the tension springs 2I and 22, respectively. Each spring has secured at its lower end a pendant 23 which is provided with an opening formed therein of a diameter large enough to permit the introduction oi splayed ends of the pivoted bail 24. In operation to release the shrine tension and remove the cap and the tube trom the ask, the bail is pulled outwardly and down wardly from its position shown in Fig. 3. llhe the bail 24 is initially moved downwardly.. ends 25 move inwardly toward the ears IB nd I8 of the collar to a position in line with the i pivotal axis 2U of the bail 24 and' the center line of said ears. In moving the ball, the springs 2| and22 are :further tensioncd since the ends 25 were originally in. a position one side l the pivot 20. Further movement of the bail re duces the spring tension since the ends 25 oi the bail have now passed the pivot point 2li. llibviously, the bail 24 is resiliently maintained in the position illustrated in Fig. d by virtue oi' the spring tension which acts upon the bail envia tending to .move the bail about its pivot` a clockwise direction as 'viewed in 3. linie cu; securing arrangement is useful for eiectiveh hlbiting direct transfer of heat from the cla ing device to the ferruled end of the Dewar When the cap is so retained in position, the closed end of the brass tube i4 extends within the flask and into contact with `the liquid rn, ntained within the body portion of the ilasl-. ibupported within the closed end of the tube is an electrical heating element 40 and a thermo-re sponsive device which comprises a bulb ill filled with carbon dioxide or some other iluid suitable for expansion and contraction with temperature variations. The conductors 32 for connecting the electrical heating element to a suitable source of electrical potential and the tube 33 which communicate with the interior of the carbon dioxide bulb 3| are each brought up inside of the brass tube. Since the closed end of the tube I4 is in contact with the cold liquid oxygen, it is desirable to prevent convection oi atmosphere through the tube because the water vapor present in the atmosphere would condense upon contact with the cold surface` of the tube and would eventually damage the heating element 40 located therein. In order to close off the end of the tube I4, there are provided a plurality of fibre washers 36 and 36', each having openings through their centers large enough to permit the passage therethrough of the conduit 38 for the conductors 32 and the tube 33 which communicate with the thermo-responsive device 30. The conduit 38 and tube 33 are each threaded through these washers which are placed at the upper end of the tube after. having been thoroughly impregnated with liquid latex. A small amount of plastic gum rubber is wound about each of the conduit and the tube and a compression nut 35 is screwed down firmly on the threaded end of the flanged tube I4, compressing the fibre washers 3B and 36 between the nut and the tube and pressing the gum rubber firmly about the conduits to form a gas-tight seal of the interior of'said tube. The freeconvention of the atmosphere being prevented by the sealing above described, there is provided in the tube a member 31 of high thermal conductiveness which contacts both the heating element 4U and the bulb 3l 'to form `a good heat-'conductive path from the heating element to the thermo-responsive device.

lilectrical power for energizing the resistance heating element 40 is obtained from a suitable source s as shown in Fig. 2. The circuit for the heating element is complete through the serially connected switches 42 and 4I. One conductor 43 leading from one terminal of the supply source is connected to the arm 44 of a single pole double throw switch When the arm 44 is in the position shown in broken line and in contact with the switch terminal t5, the pilot light 43 is connected across the supply source and indicates that the series connection to the heating circuit 4D has been brolten at the switch 4I. When the switch arm 4l is in the position shown in full line, in contact with the terminal 46, the circuit ls conditioned so that it may be completed through the switch contacts arm 41 and the terminal 48 ci the switch t2.

As illustrated in Fig. 1, each of the switches M and t2 are pressure actuated. That is the pivot arm ill of each of the switch actuating mechanisms is moved about its pivot in response to the movement ci the bellows 53 against the action ci the coiled spring 54. In the switch 4I the bellows i553 is connected to the conduit 33 leading from the the11rno-responsive device 3l, whereas the bellows 53 of the switch 42 is connected to the conduit 52 leading from, the space defined between the cap Il! and the brass tube I4. The permanent magnet M of each switch is provided for the purpose of moving the arm-5 44 and 41 with a snap action. y

The oxygen dispensing conduit connects with an opening 5I formed in the side of the cap II above the ferruled edge I2 of the flask and leads acumen into the cabinet l where it is' coiled as at 65 to provide a large hea-t exchange surface. A safety valve 53 is provided in the conduit which extends from the warming coil 65 or heat exchange surface outwardly through the side of the cabinet to the manually operated valve 56 to which is connected a flexible conduit S1 leading to the pressure regulating valve Sil;

When itis desired to use the apparatus disclosed in the present invention, the brass tube M is inserted into the connection of the Dewar flask containing the liquid oxygen. It should be noted here that this oxygen is then normally at a temperature of about -l83 C. and at atmospheric pressure, these conditions being those under which liquid oxygen is commonly stored, transported and sold to the trade. The cap lll is then securely clamped in position to provide a gas-tight seall at the ferruled edge of the flask and inner surface ll of the cap. Now if the circuit shown in Fig. 2 is connected to a suitable source of electrical potential, the switch arms Elli and il of the switch 4I and t2, respectively, will take a position shown by the full lines of Fig. 2 completing a closed series circuit through the resistance electrical heating element fill. Due to the use of the regulating valve (id, the rst result obtained by the application of heat to the liquid oxygen from heating element lil is to raise the temperature of the oxygen and store heat within it. There will be no immediate substantial evaporation of the oxygen but a rise in vapor pressure will occur at its surface. After the tein-n perature and vapor pressure have been built up considerably, the apparatus is then in condition to supply substantial quantities of gaseous oxy gen. Now when valve et is opened, the gaseous oxygen evaporated from the liquid will then. flow.

upwardly through the neck 2 to the outlet tube @il through the warming coil 55, into the ilexible dispensing tube lill and outwardly through valve 5t. As valve td allows escape of gaseous' oxy-1 gen, the vapor pressure within the flask l is reduced above the surface of the liquid oxygen but remains at a substantially nxed level below its surface. This results in an immediate replacement from the liquid of gas withdrawn from the chamber and conduits above its surface.

The electrical current will continue to flow in the heating element du until the liquid -'nass contained within the Dewar flask attains a temperature to establish equilibrium for a vapor pressure edualxto the pressure at which the pressure actuated switch 52 has been set to operate. When the vapor attains a pressure equal to or greater than the pressure setting of the switch d2, the bellows 53will have expanded sufciently to actuate the operating arm El to move the switch arm 41 from its position of engagement with the terminal 48 to open the circuit and interrupt the current iiow tothe electrical heating element 40. The switch i2 will remain in this latter position until the vapor pressure within the flask l drops below the point at which the switch 42 is adjusted to operate to close the series circuit for the heating element 4B.

It is desirable to have the pressure actuated.

switch 42 opened to an absolute pressure rather of oxygen in excess of that for which the ap paratus is designed.

The provision of the thermo-responsive switch 4i in the circuit of the heating element il@ is a safety feature of the apparatus since as long as there is a sufficient amount of liquid oxygen within the ask, the temperature of the carbon dioxide within the bulb Will be below its freezing point and the carbon dioxide will solidify reducing .the pressure Within the bellows 53 of the switch 4l'causing the switch to remain closed. However, should the supply of liquid oxygen become nearly exhausted current would still continue to flow in the heating element were it not for the provision of the thermally actuated switch y Ill. Near exhaustion of the supply of liquid oxygen permits the temperature of the carbon dioxide contained within the bulb il to increase to a value wherein the pressure is sufficient to actuate the arm il@ of the switch ll to interrupt the flow of current to the heatingelement and to connect the pilot light Ml across the supply source s to indicate to the operator the nearexhaustion of the supply of liquid oxygen.

It should be noted that since the pressure above the liquid does not depend upon ebullition from the heating element itself but depends rather upon the vapor pressure of the liquid oxygen for to build up slowly over a period of days until need for the gas is aboutto occur. ln this way there is no evaporation loss until the entire mass of liquid has attained a temperature sucient .to produce a vapor pressure over its surface aufn ficient to actuate the safety valve l'n ordinary use this safety valve would probably never function and is intended merely es safety measure in order to prevent undue pressure from being built up within the Dewar It should also be noted that the bail operated spring means previously described also performs a safety function in that the cap l@ upon a suicient increase in pressure will be caused to rise off its seat against the biasing action ci springs 22 and allow the excess pressure to escape at this point.

While the present invention is particularly lt is contemplated that improvements will be made in the Dewar flask contained herein by providing an outer shell of a self-sealing material which may seal suciently against the low vapor pressures normally used to prevent total and instantaneous escape of the oxygen should the con.. tainer be perforated by gunfire.

It will be understood that the particular form of invention disclosed is for purposes of illustration and notfor purposes of limitation, reference being `had for this latter purpose to the appended f claims.

This invention described herein may be manufactured and used by and for the Government oxygen. an electrical heating elenrieut in said courainer in heat transfer relation with said osg/en for increasing the temperature aud rute of evepc ration thereof, a, source of electrical enemy, cir cuit controlling means for connect ig' said soin-cc to scid heating element. a vapor dispensing' couduit leading from :sani coiiiiuluer, valve :necios iu. said conduit a heat y device ccuucctf to saiii conflict outside t.. ,aiueiv ami ou posed to ambient temper ture for subjecting any liquid oxygen escaping thereto to a temperature higher than the temperature of the liquiu oxygen whereby said device will he capable of operation in an inverted position.'

2, combination defined iii claim l furthe'D characterized by the fact that s circuit ce;` trolling means includes, in series, e. switc actu." ated in response to the temperature of s heatmn ing element, and a switch actuated iu response to `the pressure oi the vapor acting ou the surface of said liquid.

3. An apparatus for evaporating liquid. oxygen comprising in combination a container for calci oxygen having a restricted opening leading; to the interior thereof, means sealing' said opening comprising a. cap, a tube having open and closed ends. means securing said cap to said tube at said open end so that the closed end will project from said cap into the interior of scid containerin contact with said iiuid, scalini; means for the open end of said tube, an electrical heating element disposed within the closed end of said tube, a temperature responsive device within saisi tube, heat conductive means contacting said element and device to provide a conductive heat transfer path, circuit means for energizing said heatingr element including e. ilrst series switch connected iii thei'eu aud operated by the said ytemlceiatu1ct resuci'ifsive device, an oxygen uispeuciug coilduit leading from said cap, vulve means in salti con duit and a second series switch connecteu iu caid circuit, said second switch being ci spciisive and actuated lit* the capot within said. conduit.

.slof .rat-us for evucoratiug liquid comp a. ccuteiuer .or said liquid, pressure i'espor we een. 'a cctuated pressui'e esistiti@ tvitliiiu icl sciiti Vapor and .tu

.c heat is lost by uaporiizatiou teeming, t e, liuuici temperature 7which will d ,sirecl vapor pressure, u. Minimizing; cc cui lug said coi'ituiuei. vulve duit, and a heat exchanger located o.l seit. container, exchanger be tact with sui-rounding uit and. connect-c tu .salti dispensing conduit for cruising the vapor crees-ure to `he increased to a 'value iu excess'oi' the impor or estu-e existing on ,said liquid when calci iiquid and. vapor: are iu equilibrium whereby to permit the inverted operation of said apparatus.

El. Apparatus for vauoriziug liquid oxyueu comw pricing en insulated ooutaiiier for said liquid, oxygen, outlet' means :from said container, salu cutiet means including' a heat exchanger iocated outside of said container kin coutact with the surrounding cir, valve means in said outlet rue-aus, and means for applying; heat to .said liquid oxygen within said container.

.Apparatus for vaporizing liquid oxygen com prising a container im said oxygen iid ccntaiuer having a neck portion, a ccp i er closing: .seid neel; portion, a uispensing comu-lt com nected through said cap member into said heck portion, valve means in said dispensing conduit, and means resilieutly holding' said cap member upon said neck portion.

JOHN A. MATHIS. ROLAND WV. WLAN. 

